A method for identifying vertical zoning in metamorphic buried-hill reservoirs by logging

Abstract

The application discloses a metamorphic rock buried hill reservoir longitudinal zoning logging identification method, which comprises the following steps: collecting element logging, imaging logging and conventional logging data of sample wells in different structural positions of a research area, and preparing a single-well comprehensive columnar graph; dividing the longitudinal structural units of the metamorphic rock reservoir of the sample wells by using the fracture development characteristics and the longitudinal variation characteristics of the chemical alteration index; optimizing the logging curves which have obvious distinguishing effects on each longitudinal structural unit, and constructing a fracture dissolution index calculation formula which reflects the fracture dissolution degree; scaling the fracture dissolution index limit range of each longitudinal structural unit of the sample wells, and establishing a fracture dissolution index zoning model of the metamorphic rock buried hill reservoir; and calculating the fracture dissolution index curve of a to-be-zoned well section by using the fracture dissolution index calculation formula, and dividing the longitudinal structural units of the buried hill according to the fracture dissolution index zoning model of the metamorphic rock buried hill reservoir. The application can accurately and quickly identify the longitudinal structural units of the metamorphic rock buried hill reservoir, has the advantages of simple operation, high precision and less influence of human factors.

Description

Technical Field

[0001] The invention belongs to the technical field of well logging geology in the petroleum exploration industry, and particularly relates to a method for vertical zoning well logging identification of metamorphic rock buried hill reservoirs. Background Art

[0002] Metamorphic buried-hill reservoirs are characterized by minimal burial depth, large distribution areas, and high productivity. In recent years, significant oil and gas exploration discoveries have been made in Archean metamorphic rocks in the Bohai Bay Basin, demonstrating broad exploration prospects. Weathering and leaching are key factors controlling the development of metamorphic buried-hill reservoirs and are also a key factor in their vertical zoning. Therefore, studying the vertical zoning of metamorphic buried-hill reservoirs is of great practical significance for reservoir formation mechanisms and reservoir prediction.

[0003] There are currently two commonly used methods for dividing metamorphic rock buried hills into vertical zonations. One is a qualitative division based on petrological data such as cores, wall cores, and thin sections; the other is a qualitative division based on the morphological characteristics of deep lateral resistivity baselines and acoustic time difference curves.

[0004] Classification based on petrological data involves dividing the buried hill vertically into distinct structural units based on the degree of weathering and leaching, which partially dissolves the rocks near the top of the metamorphic buried hill along fractures. However, this method often results in significant errors and is difficult to compare across wells, as core and wall core data are discrete and discontinuous, and classification is based on subjective judgment based on the degree of dissolution and diagenetic phenomena in these cores and wall cores. This severely limits its effectiveness.

[0005] The resistivity baseline method selects several extreme points in the metamorphic buried hill where the resistivity curve reaches or approaches its maximum value. A vertical line is drawn from these extreme points. The location where the resistivity first approaches or reaches the internal resistivity baseline is considered the boundary between the weathering crust and the buried hill interior. The acoustic transit time morphology method identifies the boundary between the weathering crust and the interior as the location where a "straight, low-amplitude, micro-dentation" curve first appears. Both methods are subject to significant subjectivity in the selection of the "resistivity baseline" and the assessment of the "straight, low-amplitude, micro-dentation" acoustic transit time morphology, limiting the accuracy of zoning results and making them less suitable for fine-grained zoning.

[0006] Patent CN112302623A discloses a method for delineating the weathering crust structure of granite buried hills based on well logging data. This method constructs a structural delineation curve (FJG) parameter and intersects it with the deep lateral resistivity (RD). This method establishes a quantitative criterion for distinguishing the granite weathering crust structure, dividing the granite buried hill weathering crust into weathered clay zones, weathered conglomerate zones, weathered fracture zones, and bedrock fracture zones. This method avoids some subjective judgments and makes the results more objective. However, because metamorphic buried hill reservoirs are more heterogeneous than granite, more refined vertical zoning is required in metamorphic buried hill exploration practice. The rock electrical characteristics of the two differ significantly, making the weathering crust structure identification chart established by this method unsuitable for vertical zoning of metamorphic buried hills.

[0007] Imaging logging has important applications in identifying metamorphic buried-hill reservoirs. It can identify the occurrence, density, and aperture of fractures, distinguish between various geological features such as caves, pores, and fractures, and determine the fracture type and its effectiveness. It has the advantages of being intuitive and vertically continuous. Zoning buried-hill reservoirs based on the vertical distribution characteristics of fractures is a feasible option. However, due to the high cost of imaging operations, it is currently only carried out in newly drilled key exploratory wells.

[0008] The degree of weathering and leaching is an important indicator for buried-hill zoning. As rocks undergo weathering and leaching, minerals with poor weathering resistance undergo alteration, increasing rock fragmentation and crack opening. The chemical alteration index (CIA) measures the degree of weathering of feldspar minerals into clay minerals and is an important indicator of the degree of chemical weathering. Therefore, using elemental data to calculate the CIA to assess the degree of weathering and leaching is an effective method for buried-hill zoning.

[0009] Conventional logging is an essential item for buried-hill drilling. Imaging logging and element logging both have the advantage of vertical continuity. Therefore, combining conventional logging with element logging and imaging logging makes it possible to achieve accurate and efficient vertical zoning of metamorphic buried-hill reservoirs. Summary of the Invention

[0010] The present invention is proposed to solve the problem of difficulty in dividing metamorphic buried hill vertical zones in the prior art, and its purpose is to provide a method for logging and identifying vertical zones of metamorphic buried hill reservoirs.

[0011] The present invention is achieved through the following technical solutions:

[0012] A method for vertical zoning logging identification of metamorphic buried-hill reservoirs comprises the following steps:

[0013] (I) Collect element logging, imaging logging and conventional logging data from sample wells at different structural locations in the study area and produce a comprehensive histogram of a single well;

[0014] (II) Using the fracture development characteristics and the vertical variation characteristics of chemical alteration index to divide the metamorphic reservoir vertical zoning structural units of the sample wells;

[0015] (III) Selecting the logging curves that have a significant effect on distinguishing each vertical structural unit and constructing a calculation formula for the fracture dissolution index that reflects the degree of fracture dissolution;

[0016] (IV) The fracture dissolution index boundaries of each vertical structural unit of the sample wells were calibrated using the box plot method to establish a fracture dissolution index zoning model for metamorphic buried hill reservoirs;

[0017] (V) Calculate the fracture dissolution index curve of the well section to be zoned using the fracture dissolution index calculation formula obtained in step (III), and divide the buried hill into vertical structural units based on the fracture dissolution index zoning model of the metamorphic rock buried hill reservoir established in step (IV).

[0018] In the above technical solution, the different structural positions in step (I) include structural highs, slope parts and low parts; the imaging logging data include but are not limited to the density P10 and aperture FVA of the fracture; the conventional logging data include logging curves, and the logging curves include but are not limited to deep lateral resistivity curves, neutron curves, density curves and acoustic time difference curves.

[0019] In the above technical solution, the fracture development characteristics in step (II) refer to the end position of the continuous fracture development section interpreted by the imaging logging in the vertical direction of the single well as the boundary position between the weakly weathered fracture zone and the bedrock fracture zone; the longitudinal change characteristics of the chemical alteration index refer to the end position of the downward decreasing trend of the chemical alteration index calculated using elemental data or the top interface of the relatively straight section as the boundary position between the strongly weathered fracture zone and the weakly weathered fracture zone; the longitudinal structural units of the metamorphic rock reservoir include the sandy gravel zone, the strongly weathered fracture zone, the weakly weathered fracture zone and the bedrock fracture zone.

[0020] In the above technical solution, the logging curves that have a significant effect on distinguishing the vertical structural units in step (III) include deep lateral resistivity curves, density curves and acoustic time difference curves.

[0021] In the above technical solution, the calculation formula of the fracture dissolution index in step (III) is:

[0022] F r =DT / (SQRT(RD)*ZDEN),

[0023] Where, F r =DT represents the fracture dissolution index, which is dimensionless; DT represents the acoustic time difference, which is in μs / ft; RD represents the deep lateral resistivity, which is in Ω·m; ZDEN represents the density, which is in g / cm 3 .

[0024] In the above technical solution, the fracture dissolution index zoning model of the metamorphic rock buried hill reservoir in step (IV) is specifically divided into: the well section with a fracture dissolution index Fr value below 1 is a bedrock fracture zone, the well section with a fracture dissolution index Fr value between 1 and 2.5 is a weakly weathered fracture zone, and the well section with a fracture dissolution index Fr value above 2.5 is a strongly weathered fracture zone and a sandy gravel zone.

[0025] The beneficial effects of the present invention are:

[0026] The present invention provides a method for identifying the vertical zoning of metamorphic buried-hill reservoirs by logging, which can accurately and quickly identify the vertical structural units of Archean buried-hill reservoirs. Compared with traditional methods, a fracture dissolution index reflecting the degree of fracture dissolution is constructed. This parameter has a good correlation with the fracture aperture and has important characterization significance for the vertical weathering degree of the buried-hill reservoir. It realizes the semi-quantitative division of the vertical zoning of the metamorphic buried-hill reservoir. The method has the advantages of simple operation, high precision, and less influence of human factors. The division of each vertical structural unit is more accurate and reliable, and the comparison between different well areas is more convenient and efficient, providing a reliable basis for clarifying the formation mechanism of the weathering crust of the metamorphic buried-hill and reservoir prediction. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a flow chart of the vertical zoning well logging identification method for metamorphic buried hill reservoirs of the present invention;

[0028] Figure 2 This is a diagram of the vertical zoning structural units and their combination patterns of the metamorphic buried hill reservoir in the present invention;

[0029] Figure 3 This is the effect diagram of the conventional logging curve in the present invention on distinguishing the vertical structural units of the metamorphic rock buried hill;

[0030] Figure 4 is a regression relationship diagram between the fracture dissolution index parameter and the fracture aperture constructed in the present invention;

[0031] Figure 5 This is a model diagram for dividing the fracture dissolution index of the vertical structural unit of the metamorphic buried hill reservoir in the present invention;

[0032] Figure 6 It is an implementation status diagram of an application example of the present invention.

[0033] For ordinary technicians in this field, other relevant drawings can be obtained based on the above drawings without any creative work. DETAILED DESCRIPTION

[0034] In order to enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be further described below with reference to the accompanying drawings and through specific implementation methods.

[0035] Embodiment 1

[0036] As Figure 1 shown, a metamorphic rock buried hill reservoir longitudinal zoning logging identification method comprises the following steps:

[0037] (I) collecting element logging, imaging logging data and conventional logging data of sample wells in different structural positions in the research area, and preparing a single well comprehensive columnar graph;

[0038] The different structural positions include structural high points, slope parts and low parts;

[0039] The imaging logging data include but are not limited to the density P10 and opening FVA of fractures;

[0040] The logging curves include but are not limited to deep lateral resistivity curve RD, neutron curve CNCF, density curve ZDEN and acoustic wave time difference curve DT;

[0041] (II) dividing the longitudinal zoning structure unit of the metamorphic rock reservoir of the sample well by using the fracture development characteristics and the longitudinal variation characteristics of the chemical alteration index;

[0042] The fracture development characteristics refer to the position where the continuous fracture development section of the single well longitudinal imaging logging interpretation ends as the boundary position of the weak weathering fracture zone and the bedrock fracture zone;

[0043] The longitudinal variation characteristics of the chemical alteration index refer to the position where the downward decreasing trend of the chemical alteration index CIA calculated by using the element data ends or the top boundary of the relatively flat section as the boundary position of the strong weathering fracture zone and the weak weathering fracture zone;

[0044] The longitudinal zoning structure unit includes a sandy gravel zone, a strong weathering fracture zone, a weak weathering fracture zone and a bedrock fracture zone;

[0045] The continuous fracture development section includes a strong weathering fracture zone and a weak weathering fracture zone, the strong weathering fracture zone has serious rock alteration and developed dissolution pores and fractures, and is mainly characterized by large fracture density and fracture opening, the weak weathering fracture zone has weak rock alteration and local dissolution along the fractures, and is mainly characterized by reduced fracture opening, the bedrock fracture zone has relatively fresh rock and underdeveloped fractures, and the fractures are distributed in clusters in a discontinuous manner;

[0046] The chemical alteration index CIA calculation formula is: CIA = n (AL2O3) x 100 / [n (AL2O3) + n (CaO * ) + n (Na2O) + n (K2O)], wherein n (AL2O3), n (CaO * ), n (Na2O) and n (K2O) represent the mole fractions of AL2O3, CaO * , Na2O and K2O, CaO *is the CaO in silicate, that is, the CaO in the whole rock minus the chemically deposited CaO; n(CaO * ) is calculated and corrected as follows: n(CaO * )=n(CaO)-(10 / 3×n(P2O5)), and if the corrected n(CaO * ) is less than n(Na2O), then the corrected n(CaO * ) as CaO * Otherwise, n(Na2O) is used as the molar fraction of CaO * The mole fraction of (cited from the literature: Liu Bing, Xu Bei, Meng Xiangying, Kou Xiaowei, He Jinyou, Wei Wei, Mi He. Study on the chemical alteration index of the Neoproterozoic strata of the Tarim Plate and its significance [J]. Acta Petrologica Sinica, 2007, 23(7): 1664-1670.). The calculation formulas for n(AL2O3), n(CaO), n(Na2O), n(K2O) and n(P2O5) are: n(AL2O3)=ω(AL) / (2×M(AL)), n(CaO)=ω(Ca) / M(Ca), n(Na2O)=ω(Na) / (2×M(Na)), n(K2O)=ω(K) / (2×M(K)), n(P2O5)=ω(P) / (2×M(P)), where ω(AL), ω(Ca), ω(Na), ω(K), ω(P) are the mass fractions of aluminum, calcium, sodium and potassium, respectively, in %; M(AL), M(Ca), M(Na), M(K), M(P) are the relative atomic masses of aluminum, calcium, sodium and potassium, respectively.

[0047] like Figure 2 As shown in the figure, the vertical zoning structural units of metamorphic buried-hill reservoirs include sandy gravel zone, strongly weathered fracture zone, weakly weathered fracture zone and bedrock fracture zone. There are five combination modes of vertical zoning of metamorphic buried-hill reservoirs: type I, type II, type III, type IV and type V. The vertical structure of type I is sandy gravel zone + strongly weathered fracture zone + weakly weathered fracture zone + bedrock fracture zone; the vertical structure of type II is sandy gravel zone + weakly weathered fracture zone + bedrock fracture zone; the vertical structure of type III is strongly weathered fracture zone + weakly weathered fracture zone + bedrock fracture zone; the vertical structure of type IV is weakly weathered fracture zone + bedrock fracture zone; the vertical structure of type V is bedrock fracture zone.

[0048] (III) Selecting the logging curves that have a significant effect on distinguishing each vertical structural unit and constructing a calculation formula for the fracture dissolution index that reflects the degree of fracture dissolution;

[0049] The effect of conventional logging curves on distinguishing vertical structural units of metamorphic buried hills is shown in the figure below. Figure 3 As shown, from Figure 3It can be seen that the logging curves with obvious effects on distinguishing the vertical structural units of each metamorphic buried hill reservoir are the deep lateral resistivity curve RD, density curve ZDEN and acoustic time difference curve DT;

[0050] The fracture dissolution index F r The calculation method is to divide the acoustic time difference DT by the product of the square root of the deep lateral resistivity RD and the density ZDEN, that is, the fracture dissolution index calculation formula is: F r =DT / (SQRT(RD)*ZDEN), where F r =DT represents the fracture dissolution index, which is dimensionless; DT represents the acoustic time difference, which is in μs / ft; RD represents the deep lateral resistivity, which is in Ω·m; ZDEN represents the density, which is in g / cm 3 ;

[0051] from Figure 4 It can be seen from the regression relationship diagram of the fracture dissolution index parameter and the crack opening that the fracture dissolution index F r It has a good linear regression relationship with the crack opening FVA: F r =72.996*FVA+0.5, where FVA is the crack opening in mm, R 2 To evaluate F r The parameter related to FVA is a measure of the degree of fit of the regression equation in statistics, and is calculated using R 2 Indicates that R 2 =0.7272.

[0052] (IV) Calibrate the fracture dissolution index boundary range of each vertical structural unit of the sample well and establish a fracture dissolution index zoning model for metamorphic buried hill reservoirs;

[0053] like Figure 5 As shown in the figure, the semi-quantitative vertical zoning model of metamorphic buried-hill reservoirs based on the fracture dissolution index is specifically divided into: the fracture dissolution index of the bedrock fracture zone is less than 1, 1≤; the fracture dissolution index of the weakly weathered fracture zone is less than 2.5; and the fracture dissolution index of the strongly weathered fracture zone is ≥2.5.

[0054] The complete metamorphic buried-hill reservoir structural unit vertically includes: sandy gravel zone, strongly weathered fracture zone, weakly weathered fracture zone, and bedrock fracture zone. The sandy gravel zone is the topmost unit of the metamorphic buried-hill vertical zoning. Its rock structure is gravelly, significantly different from the massive bedrock of the buried-hill. It is easy to identify through thin-section logging and wellbore coring data.

[0055] The well section with fracture dissolution index ≥2.5 includes a strongly weathered fracture zone and a sandy gravel zone. The box plot analysis of this application method reveals that these two structural units cannot be distinguished ( Figure 5However, the distinction between these two and the weakly weathered fracture zone can be achieved through the technical solution of this application; for well sections with a fracture dissolution index ≥ 2.5, it is easy to distinguish the strongly weathered fracture zone from the sandy gravel zone through petrological data;

[0056] (V) Calculate the fracture dissolution index curve of the well section to be zoned using the fracture dissolution index formula obtained in step III, and divide the buried hill into vertical structural units based on the fracture dissolution index zoning model of the metamorphic rock buried hill reservoir established in step IV.

[0057] The present invention was applied to well sections such as B19-6-B (3875-4466m), B19-6-D (4400-4766m), B19-6-J (4574-5500m), B19-6-M (4508-5079m), BZ26-6-A (3124-3291m), BZ26-6-D (3747-4053m), BZ26-6-B (3820-4479m), and BZ26-6-E (3755-4420m). The division results of the proposed semi-quantitative longitudinal zoning method for metamorphic buried-hill reservoirs were consistent with the division results of the buried-hill zoning based on comprehensive analysis methods such as imaging logging, element logging, and thin sections at a rate of 91%, with an error generally between 3 and 20m. The method achieved good application results and is worthy of promotion and application.

[0058] Application Examples

[0059] Taking the Archean strata at 3820-4479 m in Well BZ26-6-B as an example, Figure 6 As shown in the figure, the traditional method of vertical zoning of metamorphic buried-hill reservoirs is difficult to accurately identify the buried-hill structural units:

[0060] (1) According to the resistivity value first approaching or reaching the internal resistivity baseline method as the boundary between the weathering crust and the bedrock zone, it is judged that the top interface of the bedrock fracture zone is around 4250m ( Figure 6 (shown in lane 6);

[0061] (2) Based on the position where the “straight low-amplitude micro-tooth-like” curve of the acoustic time difference first appears as the boundary between the weathering crust and the bedrock zone, it is judged that the top interface of the bedrock fracture zone is around 4050 m ( Figure 6 (shown in lane 7);

[0062] (3) Application structure partition curve F JG The zone above 4050m is judged to be a weathered gravel zone, and the zone between 4050-4479m is judged to be a weathered fracture zone, which is inconsistent with the actual situation and fails to show a clear response to the boundary near 4250m. Figure 6 (shown in lane 13).

[0063] The method of this application is used to construct a fracture dissolution index indicator curve that is of great significance for the degree of dissolution of metamorphic rock fractures, and semi-quantitative identification is performed based on a semi-quantitative vertical zoning model of metamorphic rock buried hill reservoirs based on the fracture dissolution index.

[0064] Figure 6 Tracks 8 and 9 from the center left show imaging logging data for fracture density and fracture aperture, respectively. Fracture density is measured in bars / m, and fracture aperture is measured in mm. Based on the characteristics of the imaging logging fracture density and aperture data, the continuous fracture zone ends at 4250 m, marking the interface between the weakly weathered fracture zone and the bedrock fracture zone. It should be noted that imaging logging data is missing from the 4016-4049 m section, indicating severe wellbore collapse. The acoustic transit time curve and deep lateral resistivity are both pointing to the left, indicating rock fragmentation and continuous fracture development in this section.

[0065] Figure 6 The 10th track from the left in the middle is the chemical alteration index CIA calculated using element logging data. First, the element logging data is used to calculate,

[0066] n(AL2O3), n(CaO), n(Na2O), n(K2O) and n(P2O5), calculated as follows:

[0067] n(AL2O3)=ω(AL) / (2×M(Al)),n(CaO)=ω(Ca) / M(Ca),n(Na2O)

[0068] =ω(Na) / (2×M(Na)),n(K2O)=ω(K) / (2×M(K)),n(P2O5)=ω(P) / (2×M(P)), where ω(Al), ω(Ca), ω(Na), ω(K), and ω(P) are the mass fractions of aluminum, calcium, sodium, and potassium, respectively, in %; M(AL), M(Ca), M(Na), M(K), and M(P) are the relative atomic masses of aluminum, calcium, sodium, and potassium, respectively.

[0069] Then substitute the calculated result into the formula: CIA=n(AL2O3)×100 / [n(AL2O3)+n(CaO * )+n(Na2O)+n(K2O)], where:

[0070] n(AL2O3), n(CaO * ), n(Na2O) and n(K2O) represent AL2O3, CaO * , Na2O and K2O mole fractions, expressed in %, of which CaO * is the CaO in silicate, that is, the CaO in the whole rock minus the chemically deposited CaO; n(CaO * ) is calculated and corrected as follows: n(CaO* ) = n(CaO) - (10 / 3 x n(P2O5)), and if the corrected n(CaO * ) is less than n(Na2O), then the corrected n(CaO * ) is used as the mole fraction of CaO * , and vice versa, then n(Na2O) is used as the mole fraction of CaO * (Liu Bing et al., 2007).

[0071] CIA at the corresponding depth is calculated by using the elemental logging data, Figure 5 The 10th CIA discrete curve in the figure shows that there is an obvious interface at 4065m, and the position where the downward decreasing trend of the chemical alteration index CIA ends is used as the boundary position of the strong weathering fracture zone and the weak weathering fracture zone, that is, 3820-4065m is divided into the strong weathering fracture zone.

[0072] In summary, the longitudinal zoning of the Archean buried hill in the interval of 3820-4479m in the well BZ26-6-B is revealed by using the fracture development characteristics and the longitudinal variation characteristics of the chemical alteration index, that is, 3820-4065m is divided into the strong weathering fracture zone, 4065-4250m is divided into the weak weathering fracture zone, and 4250-4479m is divided into the bedrock fracture zone.

[0073] Figure 6 The 12th curve from the left in the figure is the calculated fracture dissolution index curve, and the 11th curve is the longitudinal zoning result of the buried hill. Firstly, the fracture dissolution index formula reflecting the degree of fracture dissolution is calculated by using the conventional logging curves, and the formula is: F r = DT / (SQRT(RD)*ZDEN). Then, the longitudinal zoning of the Archean interval of 3820-4479m in the well BZ26-6-B is divided according to the metamorphic buried hill reservoir semi-quantitative longitudinal zoning model based on the fracture dissolution index: the bedrock fracture zone has a fracture dissolution index less than 1, the weak weathering fracture zone has a fracture dissolution index greater than or equal to 1 and less than 2.5, and the strong weathering fracture zone has a fracture dissolution index greater than or equal to 2.5, and the division result is as follows: 3820-4068m is the strong weathering fracture zone, 4068-4243m is the weak weathering fracture zone, and 4243-4479m is the bedrock fracture zone. The division result of the above-mentioned metamorphic buried hill reservoir semi-quantitative longitudinal zoning method based on the calculation of the fracture dissolution index by using the conventional logging curves is very consistent with the division result of the buried hill according to the imaging logging and the elemental logging.

[0074] The design principle of the application is:

[0075] The design principle of the present application is based on the rock structure and dissolution difference of each longitudinal structural unit of metamorphic rock buried hill, and the interface is divided by using the fracture development characteristics and the longitudinal variation characteristics of chemical alteration index; the logging curve sensitive to the weathering karst response of metamorphic rock is optimized, a fracture dissolution index important for indicating the fracture dissolution degree is constructed, and the quantitative characterization of the fracture dissolution degree of metamorphic rock in the continuous well section is realized; on this basis, the box chart method is used to scale the fracture dissolution index limit range of each longitudinal structural unit, the fracture dissolution index zoning model of metamorphic rock buried hill reservoir is established, and the semi-quantitative division of the longitudinal zoning of metamorphic rock buried hill reservoir is realized.

[0076] The present application overcomes the problem that the longitudinal zoning of metamorphic rock buried hill lacks effective parameters and is difficult to quantitatively characterize, and innovatively constructs a fracture dissolution index derived parameter important for indicating the fracture dissolution degree, which continuously and quantitatively reflects the fracture dissolution difference of metamorphic rock, greatly avoids the interference of subjective factors in the zoning process, can realize the fine division of strong weathering fracture zone and weak weathering fracture zone, greatly improves the objectivity and accuracy of the zoning result, solves the problem that the weathering fracture zone of metamorphic rock buried hill is difficult to quantitatively and finely divide in exploration practice, realizes the transformation of the longitudinal zoning of Bohai metamorphic rock buried hill from single structure to multiple composite structure and from qualitative to semi-quantitative. It has the advantages of simple operation, high precision, less influence of human factors, convenient and efficient comparison between different well areas, and wide application prospect.

[0077] The applicant declares that the above is only a specific embodiment of the present application, but the protection scope of the present application is not limited thereto, and those skilled in the art should understand that any change or replacement within the technical scope disclosed by the present application can be easily thought by any person skilled in the art in the technical field, and falls within the protection scope and disclosure range of the present application.

Claims

1. A method for identifying vertical zoning in metamorphic buried-hill reservoirs by logging, characterized by: The following steps are involved: (I) Collect element logging, imaging logging and conventional logging data from sample wells at different structural locations in the study area and produce a comprehensive histogram of a single well; (II) Using the fracture development characteristics and the vertical variation characteristics of chemical alteration index to divide the metamorphic reservoir vertical zoning structural units of the sample wells; (III) Select the well logging curves that distinguish each vertical structural unit and construct a calculation formula for the fracture dissolution index that reflects the degree of fracture dissolution; (IV) Calibrate the fracture dissolution index boundary range of each vertical structural unit of the sample well and establish a fracture dissolution index zoning model for metamorphic buried hill reservoirs; (V) Calculate the fracture dissolution index curve of the well section to be zoned using the fracture dissolution index calculation formula obtained in step (III), and divide the buried hill into vertical structural units based on the fracture dissolution index zoning model of the metamorphic rock buried hill reservoir established in step (IV).

2. The method for identifying vertical zoning of metamorphic buried-hill reservoirs according to claim 1, characterized in that: The different structural positions in step (I) include structural high points, slope parts and low parts; the imaging logging data include density and aperture of fractures.

3. The method for vertical zoning logging and identification of metamorphic buried-hill reservoirs according to claim 1, characterized in that: The fracture development characteristics in step (II) refer to taking the end position of the continuous fracture development section interpreted by the imaging logging in the vertical direction of the single well as the boundary position between the weakly weathered fracture zone and the bedrock fracture zone; the longitudinal variation characteristics of the chemical alteration index refer to taking the end position of the downward decreasing trend of the chemical alteration index calculated using element data or the top interface of the relatively straight section as the boundary position between the strongly weathered fracture zone and the weakly weathered fracture zone; the longitudinal structural units of the metamorphic rock reservoir include the sandy gravel zone, the strongly weathered fracture zone, the weakly weathered fracture zone and the bedrock fracture zone.

4. The method for identifying vertical zoning of metamorphic buried-hill reservoirs according to claim 1, characterized in that: The logging curves used to distinguish each vertical structural unit in step (III) include deep lateral resistivity curves, density curves and acoustic time difference curves.

5. The method for vertical zoning logging and identification of metamorphic buried-hill reservoirs according to claim 1, characterized in that: The calculation formula of the fracture dissolution index in step (III) is: F r =DT / (SQRT(RD)*ZDEN), Where, F r =DT represents the fracture dissolution index, which is dimensionless; DT represents the acoustic time difference, which is in μs / ft; RD represents the deep lateral resistivity, which is in Ω·m; ZDEN represents the density, which is in g / cm 3 .

6. The method for vertical zoning logging and identification of metamorphic buried-hill reservoirs according to claim 1, characterized in that: The method for calibrating the limit range of the fracture dissolution index of each longitudinal structural unit of the sample well in step (IV) is the box plot method.

7. The method for identifying vertical zoning of metamorphic buried-hill reservoirs according to claim 1, characterized in that: The fracture dissolution index zoning model of metamorphic rock buried hill reservoir in step (IV) is specifically divided into: fracture dissolution index F r The values ​​below 1 are bedrock fracture zones, and the fracture dissolution index F r The value between 1 and 2.5 is a weak weathering crack zone, and the crack dissolution index F r Values ​​above 2.5 indicate strongly weathered crack zones and sandy gravel zones.

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